This invention relates generally to the field of satellite communication. More specifically the present invention is an optimized integrated high capacity digital satellite trunking network system, otherwise known as the Multipurpose Wideband Communications System (MPWCS) and method for linking multiple earth stations in the same or different antenna transponder footprints of the same satellite at the greatest efficiency in use of power and bandwidth, thereby eliminating the need to reconfigure the satellite transponder based on the desired downlink footprint.
Geostationary satellites provide flexible communication relay service using earth stations and satellite transponders, with satellites supporting point-to-multi-point relay service between earth stations. Satellite operators typically lease transponder capacity based upon power, bandwidth, connectivity, and coverage desired by lessees. The leasing of power, bandwidth, connectivity and coverage of the satellite in a non-optimum manner due to the sharing between different user networks results in less than the maximum satellite power and bandwidth being utilized. Further, networks have been historically developed by separate organizations responsible for provision of space segment and earth segment leading to a complex definition of interfaces and less than the highest efficiency in the total capacity which can be derived from the satellite orbit and frequency spectrum which has been assigned. Depending on a number of satellite design parameters (e.g. uplink and downlink frequencies, antenna type, antenna boresight, antenna size, and transmitter power of the satellite) the effective xe2x80x9cearth footprintxe2x80x9d of a satellite transponder has geographic limits. The geographic limits of the transponder footprint constrain the type of relay service that may be provided.
For two users that are within the same satellite transponder footprint who desire to establish a communication link, a usual and simple form of simplex service requires that the transmitting user point its earth terminal antenna at the relay satellite and transmit on an uplink frequency. Using a satellite antenna whose receive footprint includes the earth station location of the transmitting user, the satellite transponder receives the uplink frequency, translates the frequency to a downlink frequency, amplifies the signal and then re-transmits the translated and amplified signal through the same satellite antenna used to receive the signal. The downlink signal can be received by any earth terminal that is within that satellite antenna footprint. Depending on the downlink frequency, and the previously mentioned physical characteristics of the satellite, the downlink footprint may be as small as a few hundred miles in diameter or up to several thousand miles in diameter. For two users who are within the same satellite antenna footprint, this form of relay service is very effective.
For two users who are not within the same satellite antenna footprint, but are within the satellite antenna footprint of another antenna on the same satellite, other techniques are used. One technique involves providing an electronic xe2x80x9ccross-strapxe2x80x9d between two antennas/transponders on the same satellite. In this arrangement, the uplink signal from the earth transmitting station is received by one satellite antenna and the signal is translated and amplified for re-transmission by another satellite antenna, whose footprint includes the desired receiver. Using this technique, two users who are physically distant from each other and are each within small and different satellite antenna footprints of the same satellite may use a single satellite for relay service.
The problem with cross-strapping is the tied transponders remain dedicated to each other for as long as the strap remains in place. Thus, all of the signals received by the tied receiving transponder are directed to the tied downlink transponder and to the antenna associated with that transponder. If the uplink transponder and downlink transponder are not fully utilized, strapping results in unused satellite capacity and inefficient use of resources.
Various attempts have been made to address different aspects of these problems. Examples include U.S. Pat. No. 5,615,407 to Barkats, U.S. Pat. No. 4,720,873 to Goodman et al., U.S. Pat. No. 5,283,639 to Esch et al., U.S. Pat. No. 5,081,703 to Lee, U.S. Pat. No. 5,276,904 to Mutzig et al., U.S. Pat. No. 5,455,823 to Noreen et al., U.S. Pat. No. 5,633,891 to Rebec et al., U.S. Pat. No. 5,424,770 to Schmelzer et al., and U.S. Pat. No. 5,303,393 to Noreen et al.
What is needed is a satellite network that utilizes all of the available power and bandwidth of a satellite or a fleet of satellites and that permits communications to occur among users whether using the same or different communication protocols.
It is therefore an object of the present invention to create a satellite network optimized to use the full power and bandwidth of the constituent satellite, thereby providing highest capacity for operation of a digital trunking network based on the integration of the earth stations and satellite for maximum transmission efficiency.
It is a further objective of the present invention to create a high capacity satellite communications network where usage is measured by time (minutes-of-use) rather than by power or bandwidth leased by a party.
It is yet another objective of the present invention to create a global digital high capacity telecommunications network using the full power and bandwidth of multiple constituent satellites for any communications services within the field-of-view of the satellite network.
It is a further objective of the present invention to integrate multi-service satellite telecommunications using the full power and bandwidth of constituent satellites for all communications.
It is yet another objective of the present invention to provide voice, data, facsimile, video and general bit stream service using the full power and bandwidth of constituent satellites for all communications.
It is a further objective of the present invention to provide public switched telephone network services using the full power and bandwidth of constituent satellites for all communications.
It is yet another objective of the present invention to provide private branch exchange services to selected groups of users using the full power and bandwidth of constituent satellites for all communications.
It is a further objective of the present invention to provide overlay network services to selected groups of subscribers using the full power and bandwidth of constituent satellites for all communications.
It is yet another objective of the present invention to provide domestic and international telecommunications service using the full power and bandwidth of constituent satellites for all communications.
It is a further objective of the present invention to link telecommunication services of the present invention with other communications service providers and carriers.
It is yet another objective of the present invention to link telecommunication services of the present invention with other terrestrial telecommunications providers and carriers.
It is a further objective of the present invention to provide telecommunications services using the full power and bandwidth of constituent satellites for all communications when data being transmitted is either standard or non-standard telecommunications protocols such as but not limited to; ATM, frame relay, Internet, XDSL, IP, and/or mobile telecommunications protocols.
It is yet another objective of the present invention to provide protocol conversion between different standards of communications between countries and within a single country using multiple protocols.
It is still another object of the present invention to allow a user within the satellite antenna footprint of one satellite transponder to flexibly communicate with other users who are within the same or other satellite antenna footprints of a single satellite by using the uplink frequency to selectively select between users and satellite antenna downlink footprints without the need to reconfigure the satellite transponders.
It is another object of the present invention to provide this flexible communication capability for wideband high data rate communication.
An embodiment of the present invention, hereinafter referred to as MPWCS, generally comprises three spacecraft each of which is in a geosynchronous orbit at three orbital locations. Interacting with the three spacecraft are high-capacity digital earth stations. The digital modulation used is phased shift keying (PSK) and specifically 8-PSK modulation for highest bandwidth efficiency. The use of PSK dramatically increases the channel capacity in bits per Hz which can be carried within a given amount of bandwidth.
Relatively large diameter earth station antennas are used to maximize the efficiency with which satellite power is used, for example and without limitation 9 meter antennas are currently used. Further, each earth station has a relatively large high power amplifier to insure communication links are not uplink-power limited. For example and without limitation 350 watt amplifiers are currently used. Digital modems are used for all services to be supported by the system of the present invention. Compression technology is also used within the earth segment to take advantage of silent periods within a voice conversation, statistical utilization of speech activity among multiple voice channels and redundancy within individual voice channels to allow the available satellite communications bandwidth to be allocated to the largest number of voice channels consistent with maintaining high quality and consistent with meeting national and international standards where appropriate.
In a conventional satellite system, when a transponder is illuminated by multiple signals occupying different bands or channels, additional guard bands are imposed between the channels to minimize interference. The additional guard bands consume bandwidth thereby reducing the efficiency of the transponder utilization. In an embodiment of the present invention, a transponder is limited to a single carrier permitting the full bandwidth and power of the transponder to be utilized. In another embodiment, all of the transponders on the satellite are so limited thereby maximizing the power and bandwidth utilization of the satellite.
Finally, protocol conversion is implemented throughout the system so that communications using dissimilar protocols can be converted from one to another. This allows communication from regions or countries using dissimilar protocols to occur in a continuous and seamless manner. Taken together these characteristics result in a high-capacity satellite based digital trunking network.
The present invention overcomes the disadvantages of the prior art through: a) integration of earth and space segments for maximum capacity and efficiency using the available satellite orbit and frequency allocations, and b) providing integrated digital service to users on an end-to-end basis from switching center to switching center location. Further, a combination of multiple antennas and transponders on the same satellite, are linked to hybrid signal combiners, wideband receivers, and hybrid signal splitters on the satellite that are able to use a contiguous portion of both the uplink and downlink frequency spectrum. In one embodiment, the present invention uses two transponders with wideband receivers and two 80 MHZ bandwidth portions of the frequency spectrum separated by 64 MHZ to allow a user to flexibly connect an 80 MHZ bandwidth signal between two satellite antenna footprints.
In another embodiment of the present invention, a multiplexer is also used to interconnect multiple transponders, allowing a user to select the downlink footprints of more than two transponders based on the uplink frequency.
These and other objects of the present invention will be apparent to those of ordinary skill in the art after review of the detailed description, the drawings, and the claims.